Atomic Layer Deposition in Nanoporous Catalyst Materials
Atomic layer deposition (ALD) is a self-limited growth method which relies on sequential reactions of gas phase precursor molecules with a solid surface to deposit oxides, metals and other materials in an atomic layer-by-layer fashion. The unique surface-controlled chemistry of ALD enables the conformal coating of high surface area nanoporous materials and provides atomic-level control over the coating thickness. These key advantages offer ALD the ability to precisely tune the pore size and chemical surface composition of nanoporous materials, and therefore render ALD an enabling technology for the controlled atomic-scale design of supported catalysts. Following a short introduction to the basic principles of the ALD technique, experimental studies are presented that demonstrate the ability of ALD for conformal deposition in nanometer-sized mesopores and in the bulk of high surface area powder particles. Selected examples are then discussed, illustrating the versatility of ALD for tailoring nanoporous supports and engineering the presence of catalytic sites or nanoparticles on the pore walls. A specific case study shows the potential of ALD for generating acid sites in ordered mesoporous silica materials. A second case study highlights an ALD-based approach for the synthesis of uniformly dispersed anatase nanoparticles in mesoporous silica thin films, resulting in photocatalytic activity.